Beyond current positions, each is positioning himself in primary field differently. While Walker’s blue state credentials could make him acceptable to moderate Republicans, he is also tapping more into a conservative activist, and largely white, base that likes his Wisconsin record as a fighter.

Rubio, from the diverse and electorally rich Sunshine State, is appealing as a transformational candidate, one who advisers say has potential to reach beyond the GOP and appeal to independents and moderate-leaning Democrats. This week, for example, Rubio’s campaign sought to turn questions about his personal finances into a story line portraying him as an ordinary fellow with working-class values. And as a Cuban-American with a compelling biography, Rubio can wage a history-making campaign of his own to compete with Clinton’s.

Combined, their biographies make Walker and Rubio stronger together than individually, which is why they are often mentioned together when early-state voters run through their list of preferred candidates. “Walker’s and Rubio’s strength lies, in large part, because they are each other’s number two,” says one Iowa Republican operative. “More often than not, those two names are mentioned in tandem.”